1. Field of the Invention
The present invention is directed to novel water-soluble sulfonated aryl diphosphines, catalysts containing the same, processes for preparing such diphosphines and catalysts, and processes for using such catalysts.
2. General Background and Prior Art Problems
One of the major problems of homogeneous catalysis is the separation of catalyst from product. The lifetime of a catalyst in an industrial process is greatly affected by the means of separation. It has been shown that a two phase system with water soluble phosphines as ligands can be very effective to achieve easy recycling of catalysts. However, the reactivity of the water soluble catalyst is somewhat limited by the solubility of the organic substrate in aqueous phase. The synthesis of water soluble phosphines has reached a stage that it is possible now to tailor the structure of a phosphine for improved reactivity while retaining excellent water solubility for good catalyst separation.
A widely used method for synthesizing water soluble phosphines is direct sulfonation to introduce one or more sulfonate groups onto a phenyl ring bonded to phosphorus. Unfortunately the direct sulfonation often requires harsh conditions and long reaction times. The reaction produces significant amount of phosphine oxide along with phosphines with different degrees of sulfonation. All these complicate the purification of the sulfonated products and contribute to a poor yield of sulfonation products. Therefore, the conventional direct sulfonation is not very suitable for chiral and non-chiral water soluble phosphine synthesis, since a large portion of expensive chiral phosphine is going to be sacrificed in direct sulfonation. For this reason perhaps, the yields for the direct sulfonation of chiral phosphines such as BDPP and BINAP are not reported.
One of the most interesting chiral biphosphines is (R)-(+)- and (S)-(-)-2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl, BINAP. It shows exceptional enantioselectivity for asymmetric hydrogenations. The direct sulfonation of BINAP results in a mixture of phosphines with various degrees of sulfonation. The uncertainty of the sulfonated sites causes difficulties for characterization of the ligand and its metal complexes.
Thus, there is a need for new compounds which are water soluble, exhibit outstanding surface active properties in two phase catalysis, particularly in the area of two phase hydroformylation of olefins such as 1-octene, and are easily accessible by mild sulfonation conditions.